The present invention relates to hydroxy-functional polyethers. More particularly, it relates to a process to reduce propenyl polyethers in hydroxy-functional polyethers.
Polyether polyols prepared by polymerizing alkylene oxides often contain unsaturated compounds. When the alkylene ethers include propylene oxide units, 1,2-propenyl polyether is among these unsaturated compounds. Unfortunately, when these polyether polyols are used in the preparation of polyurethane products, particularly polyurethane foams, the presence of the propenyl polyethers tends to result in discoloration in the final product. Because of the undesirability of this problem, researchers have sought ways to purify the hydroxy-functional polyethers to reduce or eliminate the propenyl polyether content and thus to improve foam quality and/or marketability.
There are a variety of means of purifying polyether polyols. Certain mineral acids are used at various stages of treatment of polyether polyols in processes such as those disclosed in U.S. Pat. No. 2,996,550 to Simons; U.S. Pat. No. 4,507,475 to Straehle et al.; and Japanese Patent J56104936 (J87036052). Water, carbon dioxide and adsorbents such as magnesium silicate are used to remove alkaline catalysts in the process disclosed by Muzzio in U.S. Pat. No. 4,129,718. Water, ortho-phosphoric acid and adsorbents such as magnesium silicate are used to remove alkaline catalysts in the process disclosed by Straehle et al. in U.S. Pat. No. 4,507,475. Formic acid is used in the process disclosed by Peffer in U.S. Pat. No. 3,299,151. Each of these methods suffers certain disadvantages, generally in that they involve introducing materials that must later be removed from the polyethers.
Some polyether polyol treatments involve ion exchange resins. Purification of certain polyether polyols in some methods has involved water and certain cationic resins, as described in Japanese Patent J61043629. In the process described in German Patent 210,460, acid neutralization of a catalyst is followed by treatment with an ion exchange resin. A mercury-activated sulfonated polystyrene ion exchange resin is used in the process described in U.S. Pat. No. 3,271,462 to Earing. Certain ion exchange resins are optionally used in place of mineral acids for hydrolyzing acetals in some polyols, as shown in the process disclosed by Mills et al. in U.S. Pat. No. 2,812,360. Certain mixed resins are used to treat polyethylene glycols for human cell genetic transfection as disclosed in U.S. Pat. No. 4,650,909 to Yoakum. In the process disclosed by U.S. Pat. No. 4,355,188 to Herold et al., a polyol may be ion exchanged or neutralized after a strong base is used to treat it. The polyols are formed using metal cyanide complex catalysts.
Acidic ion exchange resins, particularly sulfonic acid ion exchange resins, are known to release acids into organic compounds. This phenomenon is discussed in, for instance, I. J. Jakovac's Catalyst Supports and Supported Catalysts, A. B. Stiles, Ed., Butterworths, Boston (1987) p. 190. Acids are, however, detrimental in certain formulations for forming polyurethanes.
Another problem encountered in conventional cation exchange resin beds is that the resin, which is in the hydrogen ion form as the acid catalyst for hydrolysis, is susceptible to deactivation due to fouling. This fouling is the result of both propionaldehyde polymer formation on the resin bead and the basicity in the polyol feed. The fouling necessitates recharging of the bed, which is time-consuming and decreases output. Another problem encountered is that the spent resin must be disposed of in an environmentally safe way, increasing toxic waste problems.
Thus, it would be useful in the art to have a process to stabilize polyether polyols by reducing or eliminating the presence of propenyl polyethers. Such method would ideally not necessitate ion exchange beds and also would not generate waste disposal problems.